The invention relates to a fuel feeding system for a multi-cylinder engine, especially a large diesel engine, in which the fuel is fed from a fuel tank by means of a high pressure pump into a pressure supply, from which it is fed further by means of injectors into the cylinders of the engine. Large diesel engines refer here to such engines that are applicable for instance for main propulsion engines or auxiliary engines for ships or for power plants for production of heat and/or electricity.
In a modern diesel engine, fuel is injected by means of fuel injecting valves or injectors directly into the cylinders of the engine. Since the injection occurs at a relatively late phase at the end part of the compression stroke, a sufficiently high pressure is correspondingly necessary for the injection. In a conventional fuel feeding system each cylinder is provided with an injection pump of its own which pumps fuel through an injection valve and an injection nozzle into the combustion chamber of the cylinder. The arrangement is expensive since it includes many separate components. In addition the pressure in the injection pumps may vary, whereby the injection into the different cylinders may correspondingly take place under different pressures and provide different amounts of fuel.
A newer solution is a so-called common rail or common pressure injection, in which the generation of pressure and the injection of fuel are functionally separated from each other. Fuel is fed by means of a high pressure pump into a common pressure supply, from which it is led through separate pipes to the respective injectors of the several cylinders. In practice the operation of an injector is electronically controlled for instance by means of a solenoid valve in order to obtain a sufficiently short and precise injection.
Especially in large engines the common rail system is attended by certain drawbacks as a consequence of the length of the common fuel rail serving as a pressure supply, since depending of the type of engine the length may be 3 m or even more. If the common fuel rail is long and narrow, severe pressure waves or pressure pulses moving back and forth appear easily in it. These affect correspondingly the amount of fuel injected into the several cylinders. In addition due to the high pressures involved the strength of a long fuel rail and thus the security of the system may become a problem. On the other hand if the common fuel rail is long and has a relatively large diameter so as to prevent the pressure waves mentioned above and the fuel rail is cooled, reheating of the fuel to its operating temperature takes longer than in the case of a narrow fuel rail. This may be a problem especially when heavy fuel oils are utilized.